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Re: mollifying generics

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On 6/29/2016 4:11 AM, Roedy Green wrote:
> Prior to generics, I could say something like this:
>
> Comparable a = "abc";
> Comparable b = "def";
>
> or Comparable a = new Long( 2 );
> Comparable b = new Long ( 4 );
>
>
> int diff = a.compareTo(b);
>
> The run time would use the corresponding compareTo method
>
> Now generics complains about an unchecked operation.

Yes.

And that is good.

The old code is not type safe.

public class ToComOrNotToComp {
	public static void main(String[] args) {
		Comparable a = "abc";
		Comparable b = "def";
		System.out.println(a.compareTo(b));
		Comparable c = new Long(2);
		Comparable d = new Long(4);
		System.out.println(c.compareTo(d));
		System.out.println(a.compareTo(d));
	}
}

gives 7 warning, but also an exception at runtime.

> Is there a way to mollify it?  I have tried what I thought were the
> obvious means.

I don't think there are any good solution, because I don't think
there should be a good solution.

A Comparable<X> can be compared to a X.

But I don't think one can assume that a Comparable<X> can be
compared to a Comparable<X>.

Or to rephrase it: your assignments are losing too much
information to make comparison feasible.

Arne

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Thread

mollifying generics Roedy Green <inquiry@mindprod.com> - 2016-06-29 01:11 -0700
  Re: mollifying generics Andreas Leitgeb <avl@logic.at> - 2016-06-29 08:33 +0000
  Re: mollifying generics Daniel Pitts <usenet@coloraura.com> - 2016-06-29 13:43 -0700
    Re: mollifying generics Daniel Pitts <usenet@coloraura.com> - 2016-06-29 13:47 -0700
  Re: mollifying generics Arne Vajhøj <arne@vajhoej.dk> - 2016-07-05 22:28 -0400

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